This invention relates generally to door closers and more particularly to devices and techniques for increasing the efficiency of a hydraulically modulated door closer by reducing friction between a hydraulic cylinder and its piston.
Typically, a hydraulically modulated door closer involves a piston moving reciprocably within a fluid containing cylinder in response to driving forces exerted upon it by a spring, a rack and pinion gear train, or compressed fluids. As the door is opened, the pinion is rotated by an arm connecting the door closer mechanism and the door and frame. Rotation of the pinion drives the rack on the piston causing it to move in the cylinder bore and to compress a powerful spring. When the door is released, the stored energy in the compressed spring urges the piston in the opposite direction. This causes the rack to drive the pinion which swings the arm and thereby closes the door.
In order that the strong spring force not slam the door, hydraulic fluid which is confined in the cylinder in front of the piston head is metered through variable orifices to permit the door to close at a controlled rate. This provides a shock absorber or dashpot type damping to the closing motion of the door.
In the operation of the door closer just described, friction forces act to decrease efficiency of the closer. These forces, in addition to causing premature wear of the closer mechanism, impede the door motion and can contribute to weaker closings. Some friction losses occur between the piston and the cylinder wall at the lateral piston surface behind the internal rack of the piston. This is because the tapered teeth of the rack and pinion create a separating force between the two members. This force distorts the piston wall slightly and displaces the piston slightly toward the cylinder wall thereby increasing frictional drag between the cylinder wall and the piston. This decreases the efficiency of operation of the closer and contributes to premature wear of the closer.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.